WETTING TRANSITIONS AND OTHER WETTING PROPERTIES OF WATER-2,5 LUTIDINE SYSTEM

The wetting behavior of the water-2,5 lutidine system has been studied around the lower consolute point (T(c)=13.1-degrees-C). We have measured contact angles and surface tensions by varying the concentration and temperature. In the diphasic region, a wetting transition has been observed at 46-47-degrees-C on a silica wall by direct observation of the solid-liquid-liquid contact angle. The perfect wetting occurs close to T(c), the wetting phase is water rich. At the liquid-vapor interface, the analysis of the values of the surface tensions shows that, close to T(c), they obey critical laws and that a lutidine rich phase perfectly wets the vapor and the water rich phase. These behaviors have been analyzed on the basis of the contact angles of the monophasic on a silica wall on both sides of the coexistence curve, and the general variation of the surface tensions. A second wetting transition has been shown on a differently washed glass surface. Reference is made to the theoretical and experimental works following the early work of Cahn.